In this study, a bilayer system composed of N-[3-trimethoxysilylpropyl]-ethylene diamine (TEDA) and protein-A on silicon wafer was prepared by a simple two-step procedure. Self-assembly deposition of TEDA at optimal conditions resulted in the formation of homogeneous self-assembled monolayers (SAMs) similar to 2.3 nm thick with the surface roughness similar to 0.38 nm. The height value of protein-A overlayer was found to be similar to 3.5 nm, which is within experimental error of the diameter of a single protein-A (3 nm). Immunoglobulin G (IgG) molecules were then immobilized on the bilayer system by protein-A - IgG specific interactions. Using this very simple approach, the IgG layer was formed almost of a monomolecular layer for longer adsorption time (similar to 100 min), and it was packed densely for adsorption time longer than 100 min, which resulted in the increase of the amount of IgG immobilized. The use of a bilayer system composed of TEDA and protein A on silicon wafer opens the door for a fundamental understanding of how protein A affects IgG orientation on the surface and also indicates a useful guide to designing surfaces for applications such as immunosensors and biochips. (C) 2012 Elsevier B.V. All rights reserved.